Control system



April 6, 1943. R. D. JUNKINS ET AL CONTROL SYSTEM Filed Sept. 50, 193814 Sheets-Sheet 1 GASES owoooooooo OOOOOOOOOOOOO CROSS OVER LINE o E S O5 aw E O BN llll o ooooooooooomYw ooooooooooo? N S m |R|||l a 7 N ETllll v m w N 8 C 2 oooowoooooooc LINE [RANSFER AIR ISnnentors RAYMOND D.JUNKINS, JOHN D. RYDER, AND JOHN F. LUHRS 0 49/60.

w E s A E R C m m C T A W.. T U A r. a A E m m S I (Zttorneg April 6,1943. R. D. JUNKINS ET AL CONTROL SYSTEM Filed Sept. 50, 1938 14Sheets-Sheet 2 w mflwlpwi lnventoxs April 6, 1943. R, D. JUNKINS ET ALCONTROL SYSTEM Filed Sept. 50, 1938 14 Sheets-Sheet 3 MN 55 7 l l l|. mm4 Q April 6, 1943. R. D. JUNKiNS ET AL CONTROL SYSTEM Filed Sept. 30,1938 14 Sheets-Sheet 4 anl tors RAYMOND D. JUNKINS,

attorney JOHN D. RYDER,AND 8H JOHN F. LUHRS \N w QN WEN? m WwNN WEN? awE WMQQQQ ll |11| J V g H W W April 6, 1943. R. o. JUNKINS ET ALCONTROL. SYSTEM Filed Sept. 50, 1938 14 Sheets-Sheet 5 AIR J PPL Y FUEL70 BUR/VERJ A 3n ne'ntors RAYMOND D. JUNKINS, JOHN D. RYDER, AND JOHN F.LUHRS (lttomeg April 6, 1943. R JUNKINS ET AL 2,315,527

CONTROL SYSTEM Filed Sept. 30, 1958 14 Sheets-Sheet 6 h 2,, h 1/5pas/574mm 3maentors RAYMQND D. JUEWQINS JOHN D. RYDER, AME) JOHN F.VLUHRS April 6,1943. F. D. JUNKINS ET AL CONTROL SYSTEM Filed Sept. 30,1938 14 Sheets-Sheet 8 FIG. l0

mmm

0 5 /0 /5 Affi/Jfd/VCE //v 0,4/M5 A7010 0 4 pmd Imventors RAYMOND D.JUNKINS, JOHN D. RYDER, AND JOHN F. LUHRS W FIG. [I

attorney [)pril 6, 1943. R. D. JUNKINS ET AL CONTROL SYSTEM Filed Sept50, 1958 14 Sheets-Sheet 9 Q m F I Inventors RAYMOND 0.. JUNKINS, JOHN,D. RYDER, AND JOHN ,F. LUHRS FIG. l3

(ittorneg Ap 6, R. D. JUNKINS ET AL CONTROL SYSTEM Filed Sept. 50, 193814 Sheets-Sheet 11 inventors JUNKHNS JOHN D. RYDER, AND JOHN F. LUHRSRAYMOND ID.

(Ittormg April 6, 1943.

R. D. JUNKINS ET AL CONTROL SYSTEM 14 sheets-sheet 12 Filed Sept. 30,1938 QQEE umkm FIG. :58

(Ittorneg v April 6 1943. R. D. JUNKINS ET AL CONTROL SYSTEM Filed Sept.30, 1938 14 Sheets-Sheet 13 w m F MS MS N\\\ m 2 0 nwskuvk uskm GttomegR. D. JUNKINS ETAL April 6, 1943.

CONTROL SYSTEM Filed Sept. 50, 1938 14 Sheets-Sheet 14 imp/5 w w m w w.m 0

QQKMYK \QUQKM. I 2 W F 3nventors JUNKINS,

35 40 RAYMOND D.

JOHN D. RYDER, AND

JOHN F. LUHRS attorney Patented Apr. 6, 1943 CONTROL SYSTEM Raymond D.Junkins, Cleveland Heights, John D.

Ryder, University Heights, and John F. Luhrs,

Cleveland Heights, Ohio, assignors to Bailey Meter Company,

a corporation of Delaware Application September 30, 1938, Serial No.232,644

14 Claims.

This invention relates to the art of measuring and/or controlling themagnitude of variable quantities, conditions, relations, etc., andparticularly such a variable condition as the density of a liquid-vapormixture, although the variable may be temperature, pressure, or anyphysical, chemical, electrical, hydraulic, thermal, or othercharacteristic.

Our invention is particularly directed to a variable condition such as,for example, the density of a flowing fluid undergoing treatment. Thevariation in the flowing fluid undergoing treatment may be epitomized asa condition change and for the purpose of this application it will beunderstood that a condition change may be either a physical or chemicalchange, or both, and that the method hereinafter outlined and theapparatus specified is designed to be effective for all such conditions.

Condition change refers to a change in the character or quality orcondition of a fluid as distinguished from a quantity change, such asrate of flow, or change in a position as, for instance, movement of thefluid from one tank to another. Moreover, whenever herein the wordtreating or treatment is used it is to be understood that any actingupon or in connection with a fluid is intended; a fluid is treated whenit is heated, when it under oes chemical change, when two or morevarying-characteristic fluids are brought together, when a fluid iselectrolized, or when its degree of ionization is changed as, forinstance, by dilution, change of temperature, etc., and in general whenanything is done in connectionwith a fluid which is qualitative asdistinguished from quantitative.

These terms qualitative and quantitative have reference to the broadestmeaning thereof when used in connection with a definition of what ismeant by condition change; for in stance the addition to or subtractionof heat from a fluid may merely cause it to expand or contract in sizeper unit of Weight, but this change is nevertheless considered asqualitative rather than quantitative. Similarly passage of electriccurrent from one electrode to another immersed in a fluid is consideredto effect a qualitative change therein Within this disclosure; in short,any phenomenon in a flowing fluid which so evidences itself as to bemeasured in the manner herein disclosed or in connection with a densitydetermination is deemed to be a condition change.

Having the foregoing in mind it will be seen that condition changes mayoccur as the result of several different operations sequentially orsimultaneously. For instance considering the change in density whichoccurs in a flowing fluid, such change may be the result of the heatingof the fluid, or of an alteration in the chemical composition of thefluid without heat being imparted thereto, or of an expansion of thefluid while flowing through a treating zone, for instance by changingthe volume per unit lineal distance of the space in which the fluid istraveling, or a combination of these eflects may cause changes in thedensity of a flowing fluid with consequent production of a variablewhich may be used as a basis for fluid processing control. It shouldnot, of course, be overlooked that similar differing conditions may alsoresult in variations in temperature, pressure, and the other factorswhich vary in a process. Moreover, a temperature change may occur in afluid entirely because of internal action and without any externalsubtraction or addition of heat, that is as a result of chemical action.

In the present invention the method and apparatus disclosed anddescribed are useful not only in the determination of density of theflowing fluid at different points of its flow path, but also in thedetermination of mean density, time of treatment, yield per pass, andother variables or conditions which may or may not depend upon the valueof density or changes in such value. Furthermore, having provided therequisite apparatus for continuously determining such variables weutilize manifestations thereof in the control of the same or other fluidtreatment or processing.

We have chosen to illustrate and describe as a preferred embodiment ofour invention its adaptation to the measuring and controlling of thedensity and other characteristics of a flowing heated fluid stream, suchas the flow of hydrocarbon oil through a cracking still. It will beunderstood however that the invention is equally as well adapted to themeasuring and controlling of variables in the processing of other fluidsand in connection with their treatment or processing, whether chemicalor physical, or both, in nature.

The heated once through path of a forced flow vapor generator, such as asteam boiler, is quite comparable to the forced flow path of hydrocarbonoil through a tube still, or cracking unit, and the invention which weillustrate and describe, preferably in connection with the treatment ofhydrocarbon oil, is to be considered as not restricted thereto but asapplicable to the generation of steam or the processing of any or allfluids.

In connection with the preferred embodiment of our invention, namely, inthe treatment or processing or hydrocarbon oil, our invention isparticularly directed and useful with divided furnace or double furnaceoperation. By this we mean that the charge fluid, whatever be itsnature, is supplied to a forced flow confined path under pressure andthat such path may comprise one or more parallel long small bore tubepassages. Preferably the path (and the fluid therein) is heated by theexternal application thereto of heat produced by the combustion of anydesired fuel. Of course the heating may be accomplished by other means,such as heat transfer from another fluid or by waste heat gases, etc.Therefore, when we speak in the claims of ing we are not to be limitedas to the form or type of heating apparatus which is disclosed anddescribed by way of illustration in the present description anddrawings.

Preferably the forced flow fluid path is divided into two portions whichmay or may not be of equal length and volume. Preferably the twoportions are subjected each to a degree or amount of heating, or ratethereof, dependent entirely upon the desired treatment or processing tobe accomplished in that portion of the path and controlled individuallyas to the particular portion of the path and such control in accordancewith characteristics of the fluid within or leaving the path. Forexample, the oil to be treated or processed will enter the path underpressure (charge), going first into a sensible heat absorbing portion orsection of the path, and then passing into a conversion section whereincracking may desirably take place.

We desirably control the heating to the sensible heat absorbing sectionseparately and individually from the heating which is applied to theconversion section. Furthermore, we determine in connection with each ofthe sections those variables, such as density, mean density, time ofdetention, yield per pass, etc., which are of ex treme interest andimportance in controlling the heating of such sections to accomplishoptimum results in the treating or processing.

It will be appreciated that the two portions mentioned of the fluid flowpath with separate control of the heating may be housed in a singlefurnace structure, or may be housed in separate furnace structures,preferably closely adjacent.

The present preferred embodiment is illustrated and described as havinga sensible heat absorbing section and a conversion section housed in asingle furnace unit with a bridge wall dividing the sections of thefurnace. It will, of course, be appreciated that many modifications orvariations may come within the scope of our contemplation, and that itis only necessary for us to illustrate and describe, by way ofillustration, a preferred arrangement and embodiment of our invention.

While a partially satisfactory control of the cracking operation may behad from a knowledge of the temperature, pressure, and rate of flow ofthe fluid stream being treated, yet a knowledge of the density, ormanifestations thereof or related thereto, of the flow stream atdifferent points in its path is of a considerably greater value to theoperator. Furthermore, as a basis for automatic control of theprocessing these variables or manifestations thereof provide highlysatisfactory motivating means. The present invention is somewhat relatedto Patents 2,217,63 i; 2,217,637, 2,217,638 and 2,217,639 to whichreference may be had.

In the treatment of water below the critical pressure, as in a vaporgenerator, a knowledge of pressure, temperature and rate of flow may besufiicient for proper control inasmuch as definite tables have beenestablished for interrelation between temperature and pressure, and fromwhich tables the density of the liquid or vapor may be determined.However, there are no available tables for mixtures of liquid and vapor.

In the processing of a fluid, such as a petroleum hydrocarbon, a changein density of the fluid may occur through at least three causes:

1. The generation or formation of vapor of the liquid, whether or notseparation from the liquid occurs.

2. Liberation of dissolved or entrained gases.

3. Molecular rearrangement as by cracking or polymerization.

The result is that no temperature-pressuredensity tables may beestablished for any liquid, vapor, or liquid-vapor condition of such afluid, and it is only through actual measurement of the in situ densityof the fluid or of a mixture of the liquid and vapor that the operatormay have any reliable knowledge as to the physical condition of thefluid stream at various points in its treatment or when subject to acondition change. In the past any attempt which has been made todetermine such conditions have resulted in history rather than news dueto the fact that they were based on the withdrawing of samples forlaboratory analysis. Such samples withdrawn from a flow path ofnecessity had to be brought down to substantially atmospheric conditionsof pressure and temperature, and at such conditions the in situ orflowing fluid relationship of liquids, gases, and vapors was by no meansthe same as under flowing conditions. For example, the vapors and gaseswould condense or become dissolved or would pass away. Furthermore, anyanalysis or test of the sample could only be accomplished afterlaborious and lengthy laboratory procedure, which meant that the resultwas obtained minutes or hours after the sample had been Withdrawn.

In contradistinction tosuch antiquated and unsatisfactory sampling andtesting the present invention continuously and accurately determines thein situ density or other characteristic, and by this we mean that suchcharacteristic or condition is determined while the fluid is in motion,while it is being treated, and under actual operating conditions oftemperature and/or pressure. Thus a continuous and immediatemanifestation of the variable or condition is available, either byvisual indication or as a position or force which may be incorporated inan automatic control system.

It will be readily apparent to those skilled in the art that thecontinuous determination of the density of such a flowing stream is oftremendous importance and value to an operator in controlling theheating, mean density, time of detention and/or treatment, as well asthe yield per pass in a given portion of the circuit, etc. A continuousknowledge of the density of such a heated flowing stream is particularlyadvantageous where wide changes in density occur due to formation,generation, and/or liberation of gases with a resulting formation ofliquid-vapor mixtures, velocity changes, and varying time of detentionin different portions of the fluid path. In fact, for a fixed or givenvolume of path, a determination of the mean density in that portionprovides the only possibility of accurately determining the time thatthe fluid in that portion of the path is subjected to heating ortreatment. By our invention we provide the requisite system andapparatus wherein a determination of such information comprises theguiding means for automatic control of the process or treatment.

While illustrating and describing our invention as preferably adapted tothe cracking of petroleum hydrocarbons, it is to be understood that itmay be equally adaptable to the vaporization or treatment of otherliquids and in other processes. For example, in the distillation ofoils, the generation of steam, and other chemical and/or physicalprocesses, wherein a fluid is subjected to a condition change, as forexample the heating of a fluid flow path. In particular, the inventionrelates to the automatic control of the treatment process, and as aspecific example thereof We have illustrated and will describe thecontrol of the rate of flow cracking still.

In the drawings:

Fig. 1 is a diagrammatic sectional elevation of a divided furnacestructure to which the invention has been applied.

Fig. 2 is a diagrammatic representation of measuring and controllingapparatus for a heated fluid stream.

Fig. 3 diagrammatically illustrates the internal arrangement ofapparatus and wiring within certain of the instrumentalities of Fig. 2.

Fig. 4 is a functional Wiring diagram of the system.

Fig. 5 is a diagrammatic arrangement of certain of the fluid pressurecontrol ap aratus in- 5;,

corporated in the preferred embodiment.

Fig. 6 illustrates a selector valve for the fluid pressure controlsystem.

Figs. 7-22, inclusive, are curves or graphs of relationships inconnection with the and particularly in reference to Figs. 3 and 4.

Referring now in particular to Fig. 1, we indicate therein indiagrammatic sectional elevation a furnace assembly comprising twoseparately heated sections discharging products of com-bustion to acommon stack. We have indicated that a bridge wall substantially dividesthe furnace structure into two separate rooms or compartments, but thatthe bridge wall does not extend to the roof bustion from one of thesections over the top of the bridge wall joining the gaseous prodnets ofcombustion from the other section, and the two streams or total gasesthen pass through a preheating section on the way to the stack.

We have illustrated diagrammatically that the walls and roof of each ofthe sections of the furnace are substantially lined with tubes and thetubes are in well known manner connected to form a continuous flow pathfor the fluid.

We indicate the charge or incoming hydrocarbon as entering at alocation. i, passing through a preheating section 4, a sensible heatabsorbing section or portion of the path, the cross-over line 2, theconversion section or portion of the path, and leaving the furnacestructure by the transfer line 3. The once through fluid path of thestill may comprise one or more parallel tube paths but in Fig. l andelsewhere in the present disclosure we consider merely a single tubepath for purpose of simplicity.

In Fig. 1 we illustrate the sensible heat absorbing section of thefurnace structure as being subjected to the heat of one or more burnersA while the conversion section of the furnace and cone and of theheating in a invention, i

whereby the gaseous products of comsponding portion of the fluid flowpath is sub jected to the heating of one or more burners B. The burnersA and B are supplied with the necessary air for combustion from anysource which may be a forced draft blower, and indicateddiagrammatically in Fig. l as having a common supply duct divided to theburners A and B. The air going to the burners A is controlled by adamper 5 positioned by a pneumatic actuator 6. while the air going tothe burners B is under the control of a damper 1 positioned by apneumatic actuator 8.

It will be appreciated that the sensible heat absorbing section and/orthe conversion section of the furnace construction may be subjected toheat of combustion or to waste heat, or otherwise. As described herein,the burner or burners A and the burner or burners B are adapted tosupply a fluid fuel, such as gas, oil, or pulverized coal. It is notnecessary to show any detailed structure as to the type of burners orthe specific arrangement of supplying air to the burners. We indicateand will refer to the fuel supply as A to the sensible heat absorbingsection and B to the conversion section.

In Fig. l, and elsewhere, the fluid flow path has three principallocations of interest in describing our invention. We indicate locationI at the point of the charge entering the system. The location 2 at thecross-over line between the sensible heat absorbing portion of the fluidflow path and the conversion portion of the fluid flow path. We indicateat 3 the discharge from the conversion section to the transfer line.Here-- inafter reference will be made to locations I, 2 or 3.

With such an arrangement as is indicated n Fig. 1 the fluid will undergoa condition change and, during such condition change, the density of thefluid will change so that the density at location 2 will be differentfrom the density at location I, and the density at location 3 willpreferably be different than at I or 2. In the sensible heat absorbingsection there may be very little or no cracking or polymerization takeplace. Preferably the cracking will take place in the conversionsection. In said section the condition change brought about by theapplication of heat through the burners B may be a physical change, or achemical change, or a combination of both.

In Fig. 2 we have diagrammatically illustrated the flow circuit of Fig.l, and in addition have diagrammatically represented the metering andcontrolling apparatus preferably applied. The forced flow path isrepresented as a single tube wherein the charge or relatively untreatedhydrocarbon passes the location i, through the sensible heat absorbingportion of the path I I, passes location 2, through the conversionportion of the path 12, and joins the transfer line after passinglocation 3. Temperatures at locations i, 2, 3 are determined bythermocoupleslli, l6, ll respectively. The rate of flow of the charge orrela tively untreated hydrocarbon is continuously measured by the rateof flow meter 2%. This is a differential responsive device connectedacross an Orifice 21 of fixed opening, and across which there exists adi-iferential known relation to rate of flow of fluid therethrough. Themeter 26 is arranged to record the rate of flow of the charge fluiddirectly upon a uniformly graduated chart and is the dictating means,adapted to position resistances, for remotely telemeteringrepresentations of diflerens tial head and of rate of flow to a centralpanel board 28 containing measuring and controlling apparatus to bedescribed in detail hereinafter.

At location 2 a differential pressure responsive device 29 is connectedto be responsive to the differential pressure existing across anadjustable orifice 3B, which latter is adapted to be positionable acrossthe flow path to vary the amount of restriction, and thereby vary thedifferential head produced for a given rate of flow. At location 3 asimilar difierential pressure responsive device 3| is connected to beresponsive to differential head produced by an adjustable orifice 32.The responsive devices 29, 3! are not recording at their transmittinglocations, that is adjacent the orifices 3U, 32. Each of the devices 29,3! however comprises a transmitter for telemetering to the panelboard 28a representation of the value of difierential head existing at location2 and'at location 3.

While the fluid flow measuring instrumentalities 25, 29 and 3| areillustrated and described as differential pressure responsive devices,it will be understood that such showing and description are illustrativeonly and not to be taken in 1a limiting sense, because fluid flowmeasuring devices, such as displacement meters, volumetric meters,Thomas meters, or the like, may be used .in the determination of fluiddensity in practicing the invention herein disclosed.

In Fig. 2 we illustrate the fuel supply line 33 leading to the burners Aand having therein a pneumatic regulating valve 34, as well as ameasuring orifice 35 across which is connected a rate of flow meter'36adapted to continuously record the rate of supply of fuel to the burnersA and to initiate a constant flow control effective upon the valve 34.At the same time the constant fioW controller 36 is connectedpneumatically through the pipe 31 to the actuator 6. Thus the controller36 and the actuator 6 comprise a fuel-air ratio control, wherein thesupply of air for combustion to the burners A is always controlledproportionate to the actual rate of supply of fuel through the conduit33. A valve 38 is provided so that the actuator 6 may be disconnectedand the damper 5 may be positioned by hand if desired.

In like manner fuel is supplied to the burners B through a conduit 39under the regulation of a valve 40 and measured by a recorder-controller42 connected across an orifice 4!. The controller 42 provides a constantflow control regulating the valve 40 and a fuel-air ratio controleffective through the pipe 43 upon the air damper actuator 8.

The control panel 28 is preferably remotely located relative to thefurnace and the transmitters 26, 29, 3|. On the panel 28 are shownvarious instrumentalities which will be described more in detailhereinafter. The thermocouples l5, l6 are wired to a temperaturerecorder 9 while the thermocouple I! is wired to a temperature recorderlil. Associated with the instrumentalities 9, ID are controllers 13, I4actuated in accordance with certain temperatures and setting up airloading pressures effective through the pipes 45, 46 respectively. Thedevices indicated at I8-23, inclusive, comprise the receivers of thetelemetering systems, for which 26, 29, 3! are the transmitters. We haveillustrated in Fig. 2 by long dash lines the electrical cablesconnecting the transmitters 26, 29 and 3! with the receivers lB-23,inclusive. We indicate in solid heavy lines the electrical connectionsbetween the thermo-.

couples :5, l6 and ii and the instrumentalities 9 and ill. We indicatepneumatic or air control pressure pipes between the devices is and I9and a. selector valve 24 and between the devices l4, 2i and 23 and aselector valve 25 by short dash lines. In like manner by short dashlines we indicate the air pressure connecting pipes between the selectorvalve 24 and the relay GT and between the selector valve 25 and therelay 48.

The relation between volume fiow rate and differential pressure (head)is:

Q:CM /2 g,"t (A).

where Q=cu. it. per sec. C=coeflicient of discharge l /I -meter constant(depends on pipe diameter and diameter of orifice hole) :acceleration ofgravity- 32.17 ft. per sec. per

sec. h=differential head in feet of the flowing fluid. The coefiicientof discharge remains substantially constant for any one ratio of orificediameter to pipe diameter, regardless of the density or specific volumeof the fluid being measured. With C, M and /2g all remaining constant,then Q varies as the \/h. Thus it will be seen that the float rise ofthe meters 25, 29 and 3i is independent of variations in density orspecific volume of the fiuid at the three points of measurement and thatthe reading on the recorder 29 may be of diiferential head directlyindicative of volume flow. If the conduit size and orifice hole size arethe same at locations and 2 for example, then the relation of meterreadings is indicative of the relation of density and specific volume;head varying directly with specific volume and inversely with density.Thus for the same weight rate of flow past the two metering location thedifferential head at location 2 will increase with decrease in densityof the fluid, and vice versa.

If it is desired to measure the flowing fluid in units of weight,Formula A becomes:

W=CM /2ghd (B) Where W=rate of flow in pounds per sec.

d=density in pounds per cu. ft, of the fiow fluid.

h=differential head in inches of a standard liq- Thus it will beobserved that, knowing the density of the fluid passing the orifice 27,we may readily determine the density of the fluid passing the orifice 30from the relation of differential pressures indicated by the meters 2%,29.

Referring to Fig. 2 the recording meters 19. 2|

and 23, located on the control panel board 26, are arranged to recordthe following variables:

(a) Density at inlet to conversion section Meter 19 (2)) Density atoutlet from conversion section Meter l9 Mean density in conversionsection Meter 21 (11) Time in conversion section Meter 21 (8) Yield perpass Meter 23 58 0 'r-sm 100 Where d1=olensity at charge (location 1)d2=density at inlet to con-version section (location 2) ds=density atoutlet of conversion section (location 3) md=mean density in conversionsection (between 2 and 3) (cfd )1=cfd of charge orifice (cfd )2=cfd ofinlet orifice h1=head in inches of water across charge orifice h2=headin inches of water across inlet orifice h3=head in inches of wateracross outlet orifice t=time in conversion section V=volume ofconversion section W=rate of flow through still in pounds per hourY/P=yield per pass S=stock factor T=mean temperature in conversionsection To solve Equations 1 to 5 inclusive, Wheatstone bridges areused. Fig. 4 is a functional diagram of the measuring circuits employed.In each bridge one resistance will be automatically varied by means of agalvanometer amplifying mechanism to maintain the bridge in balance, andit is this resistance which will vary directly proportional to one ofthe above factors and hence become a measure of that factor. Moved incorrespondence with variations in the resistance will be a pen whichwill indicate and record the value of the factor directly.

In all cases two bridges are maintained in balance by a singleamplifying mechanism. For example, referring to Fig. 4, bridge Icomprises legs R7111, Rhz,

W f )2 and Rdz. Bridge II comprises legs Rhi, Rhs,

and Rds. With these two bridges a single galvanometer G and amplifyingmechanism is used, the galvanometer and amp ifying mechanism beingperiodically switched to be connected with one bridge circuit and thenthe other.

All of the resistances in any one bridge are not necessarily in a singlemeter case. The numerals shown on Fig. 4 following each resistancedesignate the particular meter, as shown in Fig. 2 in which theresistance is located.

The numerical values of the resistances given in the various bridgeshave been determined by assumption and calculation. The actual valuesmay vary slightly from those given and would be determined fromcalibration.

Determination 0 dz From Equation 1:

(cfdz) 12 n or hi (1) In bridge I:

Rhi is proportional to in Rhz is proportional to hz (cfd 2 (cfd 2 Rmd isproportional to W03 Rdz is proportional to d2. From the equation for abridge circuit:

R h Rdz 2 f h f lz or:

(we 1 5n m Rh.

Rdz is therefore a measure of d2. This variable (dz) will be recorded ona uniformly graduated chart in meter l9 having a range of 0 to lO with te zero at the outside chart graduation.

The relation between differential head across charge orifice (hi) andRhiv is shown on Curve Fig 7. The charge orifice is fixed, and thedifferential produced thereby'is measured by a 250" max. head meter 26which varies the Rhl resistance.

The relation between diiferential head hz across the orifice 3i) and Rhzis also shown on Curve Fig. 7. The orifice 3,0 is adjustable andtherefore has a variable (cfd h depending upon the stem setting. Thedifierential produced by this adjustable orifice is measured by a 250"max. head meter 29 which varies the Rhz resistance.

The relationship between Density (chart reading) and Rdz is shown onCurve Fig. 8.

The resistance values for Rhl, Rhz and Rd: are arbitrarily chosen. Thesevalues determine the values for the f 1 aw 1 resistance shown on CurveFig. 9.

In determining Curve Fig. 9 it was assumed that the minimum (cfd )2 evernecessary would be 4.

This resistance f h f lz 1 will be at a maximum d1=50, (0711 2 :16.

Under these conditions:

10.374 50 h. a- E (7) 50 but Rd d 1n ohms (9) Therefore at (11:50; (cfd2 :16 (10) 2 2 12 111 =40.55 ohms 11 It is apparent that the resistancesshould vary directly with density and as Gigi-'2 with one On this basisthe family of curves shown on Curve Fig. 9 were drawn up. It appearsmost feasible to have the dials of these resistances graduated in unitsof resistance. For a given stem setting of orifice 30, the resistancewill then be varied in accordance with density. After the (cfol at whichorifice 30 will operate has been established the dials may be graduatedto read directly in terms of density. Actually a tapered resistance isused to spread out the curves at the higher (cfd readings.

Determination of (is From Equation 2:

r I 3 1 f 2)3z hz In bridge II:

Rhl is proportional to hl Rhs is proportional to he f l 1 enee Rd; isproportional to (la.

The remainder of the derivation is exactly the same as for d2. It willbe noted that Curves Figs. 7, 8 and 9 apply equally well.

(13 or density at the outlet of the conversion section (location 3) willbe recorded on the same chart IS with d2.

The outlet orifice 32 is adjustable and therefore has a variable (cfd hdepending upon the stem setting. The differential produced by thisorifice is measured by a 250" max. head meter 3| which varies theresistance Rhz.

Determination of md md is determined by bridge III comprising theresistances Rdzi, Rdsi, Rmd, A and R. The resistances Rd2l and Rdsi arevaried proportionately to d2 and d3 respectively. Actually, theseresistances are mechanically tied to the resistances Rdz and Rds asshown in Figs. 3 and 4, so that they are varied together.

From Equation 3 d 2 d is proportional to E-g:

Rmd therefore becomes a measure of met when the proper constants arechosen. The relation between d21-Rd21 and d31-RCZ31 is shown on CurveFig. 10. The relation between met and Rind is shown on Curve Fig. 11.Resistance R is a constant having a value of 150 ohms. These values werearbitrarily chosen. To determine A:

max. mean density=30, Rmd=60 at 1nd of 30, Rd21+Rd31=15O -30 uniformlygrad- 0 at the outside edge 1nd will be recorded on a uated chart 2|having the of the chart.

Determination of t t is determined by bridge IV comprising resistancesRt,

. Vdl RVhi and Rindi. The resistance Rmdi is mechanically tied to theresistance Rmd and is accordingly varied in proportion to changes in1nd. The resistance fix/7E is varied proportional to the square root ofhi. This resistance is located in meter 26 measuring 121. The resistanceis manually adjustable to compensate for changes in d1.

From Equation 4:

Vmd

Rt therefore becomes a measure of md when the proper constants arechosen. The relation between '\/h1 and R\/hi is shown on Curve Fig. 12.The relation between t and Rt is shown on Curve Fig. 13. The relationbetween mal and Rmdi is given by Curve Fig. 11. These resistance valueswere arbitrarily chosen. Resistance was determined as follows:

V=126 cu. ft. (Example) Max. flow:105,000#/hr. at d1=33#/cu. f-t.

(Example) Max. md=30#/cu. ft.

Under these conditions:

It is apparent that V R: Vdi

